(1) Field of the Invention
The present invention relates to a motor, and more particularly, to a motor in which a predetermined clearance is maintained between a bearing and a shaft by a magnetic field.
(2) Description of Related Art
Small motors are used in electronic products such as hard-disc drives in computers, laser beam scanners and laser printers. Bearings are used in these motors that simultaneously support load in both the radial and axial directions to make rotation of a rotor of the motor smooth.
With regard to the laser beam printer, laser beams are used to perform the printing operation. That is, a scanned image is formed on a photosensitive drum, which is responsive to light, by radiating the laser beams thereon. A rotating multi-faceted mirror system is provided to move the beams at a uniform velocity such that the beams are aligned on the photosensitive drum in an axial direction thereon.
Referring to FIG. 1, there is shown a sectional view illustrating an internal structure of a rotating multi-faceted mirror system. As shown in the drawing, the rotating multi-faceted mirror system 10 comprises a housing 11 inside of which is disposed a motor 20. A hole 11a is formed in a side of the housing 11, and a multi-faceted mirror 12 which reflects beams onto a photosensitive drum 103 (see FIG. 2) is exposed through the hole 11a. The motor 20 rotatably supporting the multi-faceted mirror 12 comprises a stator 21 and a rotor 22, the rotor 22 electromagnetically cooperating with the stator 21. The rotor 22 and the multifaceted mirror 12 are fixed on a rotating shaft 23. A bearing 25 inserted into the rotating shaft 23 is mounted on the central portion of the housing 11 so as to rotatably support the rotating shaft 23. To generate dynamic pressure between the bearing and the rotating shaft 23, a plurality of herringbone grooves 25a are formed on an outer circumference of the bearing 25. Disposed on a top of the rotating shaft 23 is an upper member 24 facing the upper end of the bearing 25. There is also formed a spiral groove 24 on a lower surface of the upper member 24 so that dynamic pressure can be generated between the upper member 24 and the bearing 25.
However, the prior art hemispherical bearing structured as described above has a drawback in that the manufacturing process is complicated. Namely, the grooves are formed at a predetermined depth using an etching process. Because many steps are needed in the process to manufacture the bearing, overall manufacturing costs are increased.
Further, when the rotor rotates on the bearing, dynamic pressure functions as a lubricant between the bearing and the rotor. However, since the amount of the clearance between the bearing and rotor is minuscule, the dynamic pressure is affected by even a small aberration. Therefore, measuring the clearance between the bearing and the rotating shaft is required, causing manufacturing costs to increase by the additional step required.